It is conventionally known that chemical prepared toners are produced by a polymerization method or an emulsification dispersion method. Among these methods, when the toner is produced by the emulsification dispersion method, a mixture containing, for example, a resin binder and a colorant is mixed with an aqueous medium and emulsified therein to obtain toner particles. However, in the emulsification dispersion method, for example, when a polyester is used as the resin binder, there tend to arise problems such as a complicated procedure, prolonged production time and failure to control well the shape of the resulting toner particles. More specifically, in the conventional method, after the polyester is dissolved in an organic solvent and then emulsified in the aqueous medium, the organic solvent must be removed from the obtained emulsion, resulting in a complicated procedure. Also, as to control of the shape of toner particles, when a di- or higher-valent metal salt is used as an aggregating agent, only spherical particles are formed owing to a too strong aggregating force thereof, resulting in difficulty in suitably controlling the shape of the toner particles. On the other hand, when a monovalent metal salt such as potassium chloride is used as the aggregating agent, a prolonged production time is required owing to a too weak aggregating force thereof.
As techniques for producing a toner by emulsifying and dispersing a resin binder in an aqueous medium and then aggregating the thus emulsified resin particles, there have been proposed, for example, the process for producing a toner for developing an electrostatic latent image in the form of toner particles made of a resin and a colorant which are obtained by dispersing resin particles obtained by polyaddition reaction or polycondensation reaction in the aqueous medium to prepare a dispersion, and salting out/fusing the resin particles contained in the dispersion in the aqueous medium (refer to JP 2004-271686A), and the toner for electrophotography which is produced by melt-kneading a toner material containing a resin binder and a colorant, dissolving or dispersing the melt-kneaded toner material in an organic solvent capable of dissolving the resin binder therein or allowing the resin binder to be swelled therewith, emulsifying the resulting solution or dispersion in an aqueous medium, and then aggregating emulsified particles contained in the obtained emulsion (refer to JP 2002-296839A).
In any of these conventional techniques, the resin binder is emulsified using the organic solvent, and the aggregating agent made of a trivalent metal salt such as aluminum sulfate is used.
In addition, there has also been disclosed the process for producing a toner for developing an electrostatic latent image which includes an emulsifying step of emulsifying a mixture containing a polyester resin and an organic solvent in an aqueous medium to form fine particles of the mixture in the aqueous medium, and a coalescing step of successively adding a dispersion stabilizer and then an electrolyte to the resulting emulsion to coalesce the fine particles (refer to JP 2003-122051A). In this method, the emulsification treatment of the resin binder is also carried out using the organic solvent.